Recently, expectations have run high for large-screen, wall-hung televisions as interactive information terminals. There are many display devices for those terminals, including a liquid crystal display panel, a field emission display and an electroluminescent display, and some of these devices are commercially available, while the others are under development. Of these display devices, a plasma display panel (hereinafter referred to as “PDP” or “panel”) is a self-emissive type and capable of beautiful image display. Because the PDP can easily have, for example, a large screen, the display using the PDP has received attention as a thin display device affording excellent visibility and has increasingly high definition and an increasingly large screen.
The PDP is classified as an AC or DC type according to its driving method and classified as a surface discharge type or an opposing discharge type according to its discharge form. In terms of high definition, large screen size and facilitation of production, the surface discharge AC type PDP has become mainstream under present conditions.
FIG. 13 is a perspective view illustrating the structure of a panel of a conventional plasma display device. As shown in FIG. 13, this PDP is constructed of front panel 1 and back panel 2. Front panel 1 is constructed by forming a plurality of stripe-shaped display electrodes 6, each being formed by a scan electrode 4 and sustain electrode 5 on transparent front substrate 3 such as a glass substrate made of, for example, borosilicate sodium glass by a float process, covering display electrodes 6 with dielectric layer 7, and forming protective film 8 made of MgO over dielectric layer 7. Scan electrode 4 and sustain electrode 5 are formed of respective transparent electrodes 4a, 5a and respective bus electrodes 4b, 5b formed of Cr—Cu—Cr, Ag or the like, and are electrically connected to respective transparent electrodes 4a, 5a. A plurality of black stripes or light-shielding films (not shown) are formed, each black stripe or light-shielding film being arranged between and parallel to a respective pair of display electrodes 6.
Back panel 2 has the following structure. On back substrate 9, which is disposed to face front substrate 3, address electrodes 10 are formed in a direction orthogonal to display electrodes 6 and are covered with dielectric layer 11. A plurality of stripe-shaped barrier ribs 12 are formed parallel to address electrodes 10 on dielectric layer 11 with each barrier rib 12 located between adjacent address electrodes 10, and phosphor layer 13 is formed to cover a side of each barrier rib 12 and dielectric layer 11. Typically, red, green and blue phosphor layers 13 are successively deposited for display in color.
Substrates 3, 9 of front and back panels 1, 2 are opposed to each other across a minute discharge space with display electrodes 6 orthogonal to address electrodes 10, and their periphery is sealed with a sealing member. The discharge space is filled with discharge gas, which is made by mixing for example, neon (Ne) and xenon (Xe), at a pressure of about 66,500 Pa (500 Torr). In this way, the PDP is formed.
The discharge space of this PDP is partitioned into a plurality of sections by barrier ribs 12, and a plurality of discharge cells or light-emitting pixel regions are defined by barrier ribs 12 and display and address electrodes 6, 10 that are orthogonal to each other.
FIG. 14 is a plan view illustrating the structure of the discharge cells of the conventional PDP. As shown in FIG. 14, scan and sustain electrodes 4, 5 of display electrode 6 are disposed with discharging gap 14 between these electrodes 4, 5. Light-emitting pixel region 15 is a region surrounded by this display electrode 6 and barrier ribs 12, and non-light-emitting pixel region 16 is an adjoining gap or region between adjacent display electrodes 6.
With this PDP, discharge is caused by periodic application of voltage to address electrode 10 and display electrode 6, and ultraviolet rays generated by this discharge are applied to phosphor layer 13, thereby being converted into visible light. In this way, an image is displayed.
For development of the PDP, higher luminance, higher efficiency, lower power consumption and lower cost are essential. A method of raising a partial pressure of Xe in the discharge gas is generally known as a method for increasing the efficiency. However, raising the Xe partial pressure not only raises discharge voltage, but also causes a sharp increase in emission intensity that results in the luminance reaching a level of saturation. For restraining the luminance from reaching the saturation level, for example, a method of increasing the thickness of the dielectric layer formed above the front substrate is known. However, increasing the thickness of the dielectric layer reduces transmissivity of the dielectric layer, thus reducing the luminance. Moreover, simply increasing the thickness of the dielectric layer raises the discharge voltage. To achieve higher efficiency, discharge in the part shielded from the frontward light needs to be minimized by controlling the discharge. For example, Japanese Patent Unexamined Publication No. H8-250029 discloses a method for improving the efficiency. According to this known method, light emission in a part masked by a metal row electrode is suppressed by increasing the thickness of a dielectric layer above this metal row electrode.
Such a conventional structure, however, has the following problem. Although light emission in a direction perpendicular to the electrode is suppressed, discharge in a direction parallel to the electrode is not suppressed, but extends to the neighborhood of barrier ribs, which lowers electron temperature accordingly. This results in reduced efficiency.
The present invention addresses such problems and aims to improve luminous efficiency.